Depth sensing is a technology for measuring depths in a scene, i.e., the distances from a sensor to points of in the scene. Types of depth sensing include measurements using structured light cameras, stereo cameras, and depth sensing cameras based on time-of-flight (TOF) measurements of the light reflected from the scene.
For example, structured light cameras illuminate the scene using spatially modulated light. Because of the physics of the light propagation, the structured light cameras have fixed angular resolution, resulting in decrease of the depth resolution as the depth of the scene increases.
A stereo camera records the same scene from two different viewpoints. The depth of each point in the scene is determined using disparities between the points of the scene as observed in two images acquired by the stereo camera. The disparities are directly related to depths. The stereo camera is a passive system, i.e., the camera does not illuminate the scene. However, the resolution of the stereo camera decreases as the depth increases.
Some TOF cameras use time-resolved sensors for determining the TOF using a shape of the reflected light. However, such sensors are expensive and include several mechanical components, e.g., scanning mechanisms, which are prone to failure.
Alternatively, it is possible to measure the TOF by integrating the amount of reflected light received after a certain time. Integrating light is simpler and cheaper than using time-resolved sensors and can be achieved, e.g., using a charged coupled device (CCD) sensor or a carbon-metal-oxide semiconductor (CMOS) sensor, see, e.g., U.S. Pat. No. 6,100,517. However, the range of depth values that such a system can determine is limited by the capacity of the sensor that integrates the light. If the energy of the transmitted pulse is too high, then nearby points in the scene cause the sensors to saturate. On the other hand, if the energy is too low, then distant points in the scene do not receive sufficient light to produce a reflection that can be detected by the sensor.
Therefore, the conventional light integrating systems have a limited dynamic range and are appropriate for limited indoor use and ill-suited for the outdoors. This is because a typical outdoors application requires much larger depth range and field of view, compared to the limited size of indoors areas. Thus, there is a need to increase the dynamic range of the light integrating systems, e.g., for determining the depths in images acquired of an outdoor scene.